This is a nice article. The tooling is getting better all the time. I’m a big fan of trace.gl, although Chrome’s Profiler/Timeline is starting to make it easier to do this kind of work.
I respect the work you’re doing on rfx and rtype, but it is a bit disingenuous to not mention the fantastic work being done on Flow and Babel-Plugin-Typecheck, which offer compile-time and run-time typechecking with the same syntax. Both are varying degrees of rough but work very well on most projects. I find myself amazed time and time again by what Flow can catch — combined with Babel, it feels like I’m not even writing the same language I was writing just a short year ago.